KR102333846B1 - Press forming method of sheet material - Google Patents

Abstract

When press-molding a molded member having a protrusion of an obstructed protruding shape on the top plate portion, it is assumed that the molded member is molded into a target shape after preliminary molding. Provided is a press forming method of a sheet material capable of forming a high-strength steel sheet into a target shape without occurrence of breakage or wrinkles by obtaining in the order of S1 and S2 described above.
S1: Discretize the projection region of the target shape into planar elements and nodes for finite element analysis.
S2: For the discretized region, a proof force is applied from the inside in the direction normal to the planar element, and deformed under the following conditions a and b
(a) the deformation of the constituting planar element is within the elastic deformation range
(b) The angle between neighboring planar elements is free to change

Description

Press forming method of sheet material

[0001] The present invention relates to a press forming method of a sheet material that can stably obtain a target shape while preventing material breakage when a member such as an automobile part is produced from a metal plate by press forming. .

In recent years, in order to reduce the weight of an automobile body due to an environmental problem, a high-strength steel sheet is often used as an automobile part.

Moreover, press molding excellent in manufacturing cost is used for manufacture of an automobile part in many cases.

However, since a high-strength steel sheet has low ductility and is easy to break when compared with a low-strength steel sheet, it is not always easy to obtain a member having a target shape by press forming.

In addition, although increasing the strength of the steel sheet used for the purpose of reducing the body weight has the same meaning as the thickness reduction of the steel sheet, there is also a problem in that the thinner the sheet thickness is, the more likely the press wrinkle is generated.

Accordingly, there is a strong demand for the development of a press forming method for suppressing breakage and press wrinkling.

Patent Document 1 and Patent Document 2 disclose a method for producing an intermediate molded body that does not cause breakage and press wrinkling, and press-molding in a subsequent step to finally obtain a product that does not break and press wrinkle. has been

International Publication No. 2017-006793 Japanese Patent Publication No. 5867657

As a method of suppressing the fracture|rupture at the time of press molding, the method of producing the intermediate-formed object with a relaxed shape as a preforming process, then performing restrike molding, and setting it as a target shape is considered effective.

Patent Literature 1 and Patent Literature 2 described above propose a construction method in which an intermediate molded body for suppressing fracture is produced, and then restrike is performed.

However, since patent document 1 utilizes the inflow and rotation of a large-scale raw material in a post process, the periphery is liberated, and it can apply only to the fracture risk part of the flange part with easy material movement.

In addition, although Patent Document 2 shows design guidelines for an intermediate molded body in order to suppress molding defects inside the product, the final shape is divided into a grid shape, or a shape change in a cross section set radially from a center of gravity is limited to the discussion of The material behavior at the time of actual restrike molding does not necessarily deform radially from the lattice partitioned direction or the centroid, but is three-dimensional in an arbitrary direction. cannot control In addition, there was a problem that a great deal of effort and time were required for implementation.

The present invention advantageously solves the above problems, and after considering three-dimensional deformation, press forming is divided into two steps, and in the first step, the target shape and the surface area are the same and the shape is preformed into a shape that is easy to form, It aims at proposing the press forming method of the board|plate material which consists of shaping|molding to a target shape without fracture|rupture after that.

That is, the summary structure of this invention is as follows.

1. When a molded member having a cross-section hat-shaped having a top plate portion, a vertical wall portion and a flange, and having a protrusion in a closed protrusion shape on the top plate portion, is press-molded from a metal plate,

First, by press forming analysis, for the top plate portion of the protrusion region, in the order of S1 and S2 described below, a preformed shape with substantially the same surface area as the target shape and easy forming is obtained,

Next, a press forming method of a sheet material, wherein the metal platelet is press-formed into the obtained preform shape, and then form-formed into a final shape targeted at the point.

S1: Discretize the projection region of the target shape into planar elements and nodes for finite element analysis.

S2: For the discretized portion, a proof force is applied from the inside in the direction normal to the planar element, and deformed under the following conditions a and b

(a) the deformation of the constituting planar element is within the elastic deformation range

(b) The angle between neighboring planar elements is free to change

According to the present invention, when forming a molded member having a hat-shaped cross-section comprising a top plate portion, a vertical wall portion and a flange, and a protrusion portion having a closed periphery on the top plate portion, from a metal plate, it is optimal using finite element analysis. It became possible to automatically design a phosphorus intermediate molded body, and as a result, it became possible to press-form from a metal platelet which does not generate|occur|produce a crack or a press wrinkle.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the shaping|molding member which has a protrusion part of a block protrusion shape in a top plate part.
Fig. 2A is a schematic diagram showing the gist of the present invention, and is an example of the shape of a target protrusion.
Fig. 2B is a view showing a state in which the protrusion is discretized into a planar element and a node.
Fig. 2C is a view showing a preliminary shape of the protrusion.
Fig. 3A is a diagram showing a state in which the periphery of the protrusion is discretized.
Fig. 3B is an enlarged view of the main part of Fig. 3A;
Fig. 4A is a diagram showing the shape of the intermediate molded body after applying internal pressure to the discretized portion.
Fig. 4B is a diagram showing a target shape of a discretized region.
Fig. 5A is a view showing a comparative method in which the first step is shallow drawing forming and the second step is bending forming with a pad attached.
FIG. 5B is a diagram showing a pad pressing position in FIG. 5A .
Fig. 6 is a view showing the rate of reduction in plate thickness when forming by the conventional method 1;
Fig. 7 is a diagram showing the reduction rate of sheet thickness when shallow drawing forming (first step) is performed in Comparative Method 1;
Fig. 8 is a diagram showing the rate of reduction in plate thickness when bending molding with a pad (second step) is carried out in Comparative Method 1;
Fig. 9 is a view showing the reduction rate of plate thickness when molded into an intermediate molded body shape according to the method 1 of the present invention.
Fig. 10 is a view showing the reduction rate of plate thickness when molded into a target shape according to the method 1 of the present invention.
11 : is a figure which shows the component shape made into the object in Example 2. FIG.
Fig. 12 is a diagram showing the plate thickness reduction rate when the target part of Example 2 is molded by the conventional method 2;
13 : is a figure which shows the plate|board thickness reduction rate at the time of carrying out shallow drawing forming (1st process) by the comparative method 2 of the target component of Example 2. FIG.
Fig. 14 is a diagram showing the reduction in plate thickness when the target part of Example 2 is subjected to padded bending molding (second step) in Comparative Method 2;
It is a figure which shows the state in which the fracture|rupture danger part vicinity of the target component of Example 2 was discretized.
Fig. 15B is an enlarged view of the main part of Fig. 15A.
Fig. 16A is a view showing the shape of the intermediate molded body after applying an internal pressure to the discretized portion.
Fig. 16B is a diagram showing a target shape of a discretized site.
Fig. 17 is a view showing the reduction rate of plate thickness when molded into an intermediate molded body shape according to the method 2 of the present invention.
Fig. 18 is a view showing the rate of reduction in plate thickness when molded into a target shape according to the method 2 of the present invention.

Hereinafter, the present invention will be specifically described.

For example, as shown in FIG. 1 , as a cross-section hat-shaped molded member comprising the top plate portion 11, the vertical wall portion 12, and the flange 13, the periphery of the top plate portion 11 is closed in a protruding shape. That is, even if the molding member 10 having a shape having the protrusion 14 of the obstructed protrusion shape is molded in one step using a press molding die, the target shape is complicated and the ductility of the material used is low. , breakage occurs in the vicinity of the protrusion, and a product having a target shape cannot be obtained.

In order to solve this problem, the method of dividing|segmenting a press forming process into a plurality may be adopted. That is, it is a method of press-molding to a gentle shape in a preliminary molding step, and performing press molding (restrike) again in order to set it as a target shape in a post-process. At this time, the design of the shape of the molded object (hereinafter, referred to as a green body or an intermediate molded body) produced in the preliminary molding process has conventionally been performed by the designer's experience and know-how.

In recent years, by taking a cross-section of a product radially from the lattice or centroid including the fracture region and deforming the cross-sectional line length within an appropriate range, expansion and contraction of the material in the restrike process is suppressed, and there is no fracture or wrinkling. Design based on the effect that a product can be obtained has come to be implemented (for example, patent document 2).

However, when the restrike is applied, the deformation of the material is rarely carried out along the cross section radially from the grid or centroid, and usually three-dimensional material movement in an arbitrary direction occurs over almost all areas. . Therefore, only to the effect of matching the cross-sectional line length described in Patent Document 2, problems of breakage and wrinkles are often caused during restrike, and in the worst case, the shape of the intermediate molded body must be determined by repeated trial and error. In some cases, it was not possible to obtain a suitable intermediate molded body shape.

Therefore, the present inventors considered to obtain an optimal intermediate molded body by using a three-dimensional finite element method as a press forming analysis in order to cope with the deformation of a three-dimensional material that cannot be coped with by using a cross-sectional line length.

EMBODIMENT OF THE INVENTION Hereinafter, the meaning of this invention is demonstrated based on FIG. 2A - FIG. 2C.

An example of the shape of the target protrusion part is shown to FIG. 2A. In Figs. 2A to 2C, a two-dimensional cross section is shown in order to make it easy to understand, but in reality, it is necessary to consider a three-dimensional shape.

Next, as shown in Fig. 2B, the protrusion regions 1 to 8 for forming the target shape are discretized into planar elements and nodes (mesh is created). In addition, in the figure, it is preferable to make the distance between each node shown by the numbers 1-8 become equal as much as possible.

Then, using the Finite Element Method, a gentle preliminary shape that facilitates final molding in the next step is obtained ( FIG. 2C ). At this time, it is preferable that each side connected at each node is free to bend, and that the obtained gentle preliminary shape and the target shape have substantially the same surface area.

That is, the preliminary shape is determined by applying a proof force to the discretized portion in the normal direction of the planar element (also referred to as a shell element) from the inside thereof. (b) The angle between adjacent planar elements is allowed to change freely.

In this way, the preliminary shape of the gentle shape as shown in FIG. 2C is determined.

Next, in actual press molding, the mold of the preliminary shape (FIG. 2C) obtained as described above is produced, the blank is molded into the preliminary shape, and then the mold is molded into the target shape (FIG. 2A) by restrike.

Next, a specific procedure using the above method will be described.

First, in the target shape shown in Fig. 1, the connecting ridge line portion between the top plate portion 11 and the vertical wall portion 12, including a portion in which fracture or wrinkling is a problem, is discretized into a planar element and a node, and the adjacent nodes are line segments and make the area enclosed by the line segment a planar element (create a mesh). This schematic diagram is shown in FIG. 3A. 3B is an enlarged view of a principal part.

At this time, although the space|interval in particular between each discretized node is not restrict|limited, It is preferable to set it as about 50 % - 300 % of plate|board thickness.

Next, a finite element analysis is performed in which the plane constituting the discretized region is deformed by applying an internal pressure from the inside of the region to the normal direction of the planar element. At this time, the deformation of each of the planar elements constituting it is made within the elastic deformation range, and the angles between the adjacent planar elements are carried out under conditions of freedom of change.

As described above, since the shape is gentler than the target shape, it is easy to form and the shape of the intermediate molded body having the same surface area as the target shape can be easily obtained. An example of the shape of the intermediate molded body obtained is shown in FIG. 4A. Fig. 4A is the shape (preliminary shape) of the intermediate molded body after applying the internal pressure, and Fig. 4B is the target shape.

The intermediate molded body thus obtained has a gentler shape than the target shape, and since local deformation and stress concentration can be avoided, fractures or wrinkles do not occur. Further, if the intermediate molded body is subsequently formed into a target shape, in this form molding, only bending deformation is applied to the respective planar elements and nodes, so that the planar elements are hardly deformed. Therefore, an intermediate molded body that does not break or wrinkle is obtained, and new expansion and contraction does not occur during press molding from the intermediate molded body to a target shape. can be obtained

Example

(Example 1)

A member having the shape shown in Fig. 1 is produced by press molding. The material is a steel plate of 1180 MPa class and a plate thickness of 1.2 mm.

In the conventional method, it was set as only one process of draw molding (conventional method 1).

Moreover, as a comparative method, as shown in FIG. 5A, the 1st process was made into shallow drawing-draw molding, and the 2nd process was made into foam molding with a pad (comparative method 1). Here, FIG. 5A shows a molding shape, and FIG. 5B shows a pad pressing position.

In the method of the present invention, the first step was draw molding and the second step was foam molding (Invention Method 1).

First, the result of molding in the conventional method 1 is shown in FIG. 6 . As shown in the figure, in the conventional method 1, a large plate thickness reduction occurs locally, and a fracture is caused from this portion.

Further, in Comparative Method 1, the result of forming the intermediate molded body by shallow drawing drawing is shown in Fig. 7, and the result of forming the pad with a pad into the target shape is shown in Fig. 8 . In the case of Comparative Method 1, local plate thickness reduction occurred in both the shallow drawing-draw molding in the first step and the pad-attached foam molding in the second step, and there is concern about fracture from this portion.

Next, in the implementation of the method 1 of the present invention, the intermediate molded body was subjected to press molding analysis by the finite element method. As shown in Figs. 3a and b, a part of the vertical wall and the top plate were discretized into planar elements and nodes. During the discretization, the interval between the nodes was set to about 1.2 mm equal to the plate thickness. Next, an internal pressure was applied in the normal direction of each planar element using finite element analysis. The result is shown in FIG. 4A. This is the shape of the intermediate molded body, and the result of producing a mold and drawing molding is shown in Fig. 9 . It turns out that a plate|board thickness decrease is relieve|moderated also compared with FIG. 7 and FIG. 8 of course with FIG. 6 and a fracture|rupture is avoided.

In addition, as a 2nd process, the result of performing foam molding with the metal mold|die which has a target shape is shown in FIG. Also in the 2nd process, it did not generate|occur|produce a significant reduction in plate|board thickness, did not reach a fracture|rupture, but confirmed that this invention is effective.

(Example 2)

A member of the shape shown in FIG. 11 is produced by press molding. The material is a steel plate of 1180 MPa class and a plate thickness of 1.2 mm.

Similar to Example 1, in the conventional method, only one step of the drawing step was used (conventional method 2).

As a comparative method, the 1st process was shallow drawing-draw molding, and the 2nd process was foam molding with a pad (comparative method 2).

In the method of the present invention, the first step was draw molding and the second step was foam molding (Invention Method 2).

First, the result of molding by the conventional method 2 is shown in FIG. 12 .

As shown in the figure, in the conventional method 2, a large plate thickness reduction occurs locally, and a fracture occurs from this portion.

Moreover, the result of shallow drawing draw molding in Comparative Method 2 is shown in FIG. 13, and the result of foam molding with pad attached is shown in FIG. 14. In the case of Comparative Method 2, a local decrease in plate thickness occurred in both the shallow drawing draw molding in the first step and the pad-attached foam molding in the second step, and fracture from this portion is also likely to occur. .

Next, in the implementation of method 2 of the present invention, the intermediate molded body was subjected to press molding analysis by the finite element method. As shown in FIGS. 15A and 15B , a part of the vertical wall and the top plate surface were discretized into planar elements and nodes. During the discretization, the interval between the nodes was set to about 1.2 mm equal to the plate thickness. Next, the result of applying the withstand pressure in the normal direction of each planar element using the finite element analysis is shown in FIG. 16A (in addition, FIG. 16B is the target shape). This was made into the shape of an intermediate molded body, and the result of shape|molding with a draw mold|die is shown in FIG. It turns out that a plate|board thickness reduction is relieve|moderated also compared with FIG. 13 and FIG. 14 as well as FIG. 12, and fracture|rupture is avoided.

18 shows a result of performing foam molding with a mold having a target shape as the second step. Also in the 2nd process, it did not generate|occur|produce a significant reduction in plate|board thickness, did not reach a fracture|rupture, but confirmed that this invention is effective.

1 to 8: each node of the protrusion region
10: molded member
11: top plate part
12: vertical wall part
13: flange
14: protrusion

Claims (1)

When a molded member having a hat-shaped cross-section comprising a top plate portion, a vertical wall portion, and a flange, and having a protrusion in a closed protrusion shape on the top plate portion, is press-molded from a metal platelet,
First, according to press forming analysis, for the top plate portion of the protrusion region, in the order of S1 and S2 described below, the target shape and the surface area are the same within the elastic deformation range, and the preformed shape is easy to form. to save
Next, a press forming method of a sheet material, wherein the metal platelet is press-formed into the obtained preform shape, and then form-formed into a final shape targeted at the point.
S1: Discretize the projection region of the target shape into planar elements and nodes for finite element analysis.
S2: For the discretized region, a proof force is applied from the inside in the direction normal to the planar element, and deformed under the following conditions a and b
(a) the deformation of the constituting planar element is within the elastic deformation range
(b) The angle between neighboring planar elements is free to change

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